Interpretive Summary: Identification of air contaminants in controlled environments is difficult because of varied spectrum of problem sources. Propylene glycol (PG) is a chemical that is commonly used in coolants and de-icing solutions for cars, airplanes, and boats. It is also used in equipment associated with controlled environment facilities, such as growth chambers, to regulate temperatures. PG was used as coolant in SPAR (Soil-Plant-Atmosphere-Research) chambers. PG leaked from the valve packing system in the air handling unit in some of the SPAR chambers where corn plants were grown. PG vapor was trapped inside the chamber and injured the corn plants. Symptoms of leaf edge chlorosis, later developing into necrosis, were observed on the third day of emergence or on the third day after moving healthy plants into the chambers. We identified this problem by using a portable photoionization detector to obtain instantaneous readings of total volatile organic compound concentrations inside the chambers. To test if PG is toxic to plants other than corn, healthy young soybean plants were grown in the chambers with or without PG leaks. Injuries on soybean leaves were observed after five days, although symptoms were slightly different. The chlorosis symptoms were not uniformly distributed on all soybean leaves. Some soybean leaves curled up and others had white spots. To avoid this problem, chamber manufacturers should separate the cooling valve packing system from the plant growing space. Researchers who use controlled environment facilities should make every effort to remove any source of contaminants from the plant growing space.

Technical Abstract:
The vapor of propylene glycol (PG), which was used as coolant in growth chambers, has been found to be toxic to corn (Zea mays L.) and soybean (Glycine max L.) plants. PG solution leaked from a valve packing system and volatilized to vapor, which was trapped in a semi-closed growth chamber. Symptoms of leaf edge chlorosis, later developing into necrosis, were observed on the third day of emergence or on the third day after moving healthy plants into the chamber. For young soybean plants, symptoms were slightly different from those observed in corn plants; the chlorosis symptoms were not uniformly distributed in all soybean leaves. Some soybean leaves curled up and others had white spots. This problem was identified by using a portable photoionization detector to obtain instantaneous readings of total volatile organic compound concentrations inside the chambers. The presence of PG was verified by using sample collection with solid phase microextraction followed by analysis with multi-dimensional gas chromatography mass spectrometry.